In devices using electric motors, such as string trimmers, the electric motor is supported inside a motor housing by a support structure. These support structures may take various forms as taught by the prior art. One type of support structure commonly used is a series of transverse support ribs which engage the sides of the electric motor and inhibit any transverse displacement of the electric motor relative to the housing. In many of these devices, the member driven by the electric motor is rotatively unbalanced and which upon rotation impart a vibration to the motor itself. The vibration of the motor produces a transverse force on the ends of the support ribs engaging the motor which, after a period of time, deforms the support ribs allowing the motor to vibrate independent of the motor housing. This latter condition results in a hammering of the ends of the support ribs by the motor further aggravating their deformation. This also increases the vibrational force transmitted to the motor housing. This deformation of the motor support ribs is accelerated when the motor housing is made from a structural plastic in which the support ribs are integrally molded into an external shell or housing.
In hand-held devices, such as a string trimmer, the increased vibration of the housing is transmitted to the user and produces an unacceptable sensation and, on occasion, produces a numbness of the user's limbs. This increased vibration also leads to catastrophic failure of the support ribs resulting in a significant shortening of the useful life of the device.
The invention is a vibration damper disposed between the electric motor and the motor housing which reduces the deformation of the support ribs, absorbs a significant portion of the vibrational energy imparted to the motor by the unbalanced driven device, reduces the amplitude of the vibration imparted to the motor housing and increases the operating life of the device.